The present invention relates to arrangements for coupling light at high efficiency between a light source and one or more light guides or optical fibers. An article by Cassarly et al., "Comparison of Dual Focus Collector Schemes for Fiber Systems," SAE Paper No. 970254, presented at the February 1997 SAE Congress, surveys arrangements for efficiently coupling light from a high brightness light source, such as an instant light, metal halide high pressure discharge lamp to light guides or optical fibers. In several of the embodiments discussed, elliptical reflectors focus light into light guides. The light guides or fibers receive light at their input ends within an angular distribution that can efficiently be transmitted through the light guide or fiber. As used herein, angles of light are measured with respect to the main direction of light propagation. The arrangements work by placing the light source at the first focus of an elliptical reflector and placing the collection optics at the second focus. The desirability of such systems are strongly dependent on the availability of high brightness, short arc (e.g., 2.7 mm), light sources. With "point-like" light sources, these systems can be made quite compact.
It would, however, be desirable to provide an efficient and compact light coupling arrangement for arc sources with longer arc gaps (e.g., 7 mm) that are not as "point-like" by employing non-focusing optical elements to achieve the reduction in the angular distribution of light transmitted from the light source to the extent desirable for efficient collection and transmission by a light guide or fiber. It would also be desirable if embodiments of light coupling arrangements using such different optical elements could be manufactured more easily and at lower costs than embodiments using elliptical (or other focusing) collectors.